Brake

[aquamantx]

Hello all,
Have a slight brake issue. when I press the rear brake pedal the brakes apply but do not release leaving bike hard to roll.
thinking either the master is bad or the proportioning vale.
Pulled the unit and it pumps fluid in both directions and has a vacuum on the return.
rebuild kit or try to redo the proportion valve.
caliper had been rebuilt.

Any ideas?

[DiverRay]

How long ago was the rebuild on the caliper and who did it?
How old are the brake lines?
I would start with the rear caliper, as it is the one not releasing. If there is a buildup of gunk/rust/etc. behind the "O" ring seal, that will cause the caliper to not release. I made a tool from a cheap, small, flat blade screwdriver to clean out the seal seating area.

[cajun31]

I make it a habit to change the fluids at a minimum every two years. The brake fluid absorbs water and does all kinds of bad things. As Ray stated the piston o rings can get crud around them. One of the main things is the spooge holes in the masters. If they get clogged the brakes don't release. The proportioning valve is a tough one. As far as I know they don't have a rebuild kit for them. The master cylinder rebuild kit can be obtained from Xj4ever.com. Just send them an email and they will quote you a price and payment method. I ordered one from them for my 81 MNS. I asked at that time about the proportioning valve and was told nothing available. Generally flushing the system and cleaning everything does the trick. Elaborate a bit on what you have done and how recently.

[aquamantx]

Calipers were a couple of years ago. They were pretty gunked up. I did the rebuild. lines are probably the original. Bike has been sitting since then. life intrudes. Fluid was changed in master at that time.
I will email xj4ever and see if I can get a kit.
looking at picking up a sonic cleaner to bust everything up on the rebuild and flushing all lines with new fluid to clear out any particles.

[cajun31]

Sounds like a plan. I might add one thing. I used to fight these brakes trying to bleed them and finally bought a mity vac. Problem solved. Well worth the investment and makes the job of replacing the brake fluid a lot more manageable. If you are by a Harbor Freight they have them as well as other less expensive options.

[aquamantx]

Thanks for the tip. Have you ever used the one way bleeder valves?. I have seen those in the past.

[Ranger_xs1100]

I'm counting on others here to correct me if I'm not quite accurate with the following troubleshooting. When the brake is dragging, if you disconnect the brake line and the drag releases, then the problem is with the master cylinder. If the brakes still drag after disconnecting the brake line, the problem is with the caliper, which it usually is from sitting for a year or two or more. If that's the case, it's a pretty sure fix by simply removing the caliper piston rubber washer/seal and clean behind it.

[DiverRay]

Ranger you are correct. Clean everything with new brake fluid, and then flush the system again. I DO use the vacuum tool from HF, and it's been working for about twenty some years.
If I remember correctly, the valve doesn't have much that would need replacing.
If you want to go with the "one way" bleeder, you WILL need to bench bleed the master EVERY TIME you work on it. The vacuum tool will usually bleed properly without the bench bleed.

[aquamantx]

Thanks for the testing advice. The XJ guys are quick. Already got a response on the email and they do have a kit.

[DEEBS11]

I must have done a hundred bike calipers over the years. It's as common a problem as gummed up carbs. Moisture forms (from years of not changing the brake fluid) under the caliper piston seal and caused aluminum oxide. It's white and powdery. It reduces the inner diameter of the bore and squeezes the piston. You grab the brakes and the hydraulic pressure is strong enough to push the piston out but it will not return.

You can take the seal out and clean out the corrosion with a pick and the re-assemble. It always works.

[DEEBS11]

To get a frozen piston out you will need a metric grease zerk and a grease gun.


https://www.ebay.com/itm/181715388977

[DEEBS11]

Clean here.

[aquamantx]

thanks for the advice.

[Larrym]

The Caliper pistons themselves (usually ferrous) can get rusted/pitted by the moisture/water too and then not move back freely against the seal(s) on the return stroke of the MC. (O_o)

All the mOaR reason to be diligent about wholesale exchanges of the brake fluid every time it looks black like coffee instead of clear like it comes outta the new/unsealed container. (_Oo)

Mity Vac? (☉_☉)

Nope. Don't got one. ┐(´～｀)┌

I use this instead-

Generates a vacuum in a much larger volume than a mity vac so no need to keep'a pumping up the mity vac to keep the vacuum constant. ʅ(́◡◝)ʃ

Also wurky fOaR those pesky middle/final drive fluid exhanges w/o having to wunder if the drain plug(s) and washers are gonna start leaking this time around. (－‸ ლ)

Best tool fOaR draining/refilling the fork oil on my 79 special with air forks. Remove valve stem cores to decompress air. Open drains at fork bottom(s). Drain oil and then wurky the front suspension a few times to get all of it out. Then hook up topsider to fork air caps and use a section of clear vinyl hose to suck up the correct amount of fork oil into the drain hole at the bottom. ( ๑‾̀◡‾́)σ"

The topsider has the v o l u m e of vacuum/air so the oil don't flow out the bottom drain hole whilst you find/grab the drain plug and thread it in. (◕‿◕)

Yah....I know. Not do-able wit the XJ or standard forkies, right? ( •_•)

Still....I've never bought or used the mity vac.... (*´_ゝ｀)

Always had/used the topsider and it's been my goto ever since I bought my XS a redonkuous number of years ago... (´～｀ヾ)

HTH. ヽ(゜～゜o)ノ

[aquamantx]

Do you know what size zerk that is?